1. Technical Field
This invention relates to a plug fabricating method especially suitable for application to fabrication of a connection hole plug and a contact plug made of tungsten.
2. Description of the Related Art
Recently, along with progressive micro-sizing of semiconductor devices, wirings are getting more and more multi-layered when manufacturing semiconductor devices. As a result, steps in manufacturing, processes of connection hole plugs and contact plugs (hereinafter generically called contact plugs) are increasing, and manufacturing processes of semiconiductor devices are getting more and more complex.
A process for fabricating a contact plug is concretely explained below.
As shown in FIG. 1, after an inter-layer insulating film 102 of SiO.sub.2 is formed on a Si substrate 101, a resist pattern (not shown) with a predetermined configuration is made on the inter-layer insulating film 102. After that, using the resist pattern as a mask, the inter-layer insulating film 102 is etched by reactive ion etching (RIE) to form a contact hole 103. The resist pattern is removed thereafter. Then, a titanium (Ti) film and a titanium nitride (TiN) film are sequentially formed on the inter-layer insulating film 102, also covering the side wall and the bottom surface of the contact hole 103, to make a direct contact layer 104 of Ti/TiN. After that, within a deposition chamber (not shown), a W film 105 is formed on the entire surface of the inter-layer insulating film 102 by blanket tungsten chemical vapor deposition (blanket W--CVD) so as to bury the inside of the contact hole 103.
Next as shown in FIG. 2, the Si substrate 101 is moved into an etching chamber (not shown), and the W film 105 is partly removed by etch-back by RIE using sulfur hexafluoride (SF6) gas as the plasma etching gas.
Next as shown in FIG. 3, the direct contact layer 104 is partly removed by etch-back to expose the top surface of the inter-layer insulating film 102 by RIE using Cl2 as the plasma etching gas. As a result, a contact plug 106 of W deposited on the Ti/Tn contact film as the base is formed inside the contact hole 103.
This conventional process for fabricating a contact plug, however, involved the following problems. That is, as reviewed above, when the contact plug 106 is formed, the direct contact layer 104 such as Ti/TiN film must be made before the W film 105 is formed by blanket W--CVD). Additionally, not limited to the Ti/TiN film mentioned above, various kinds of structures may be used as the direct contact layer 104, depending upon the process actually employed. Therefore, etch-back processing had to be done for a plurality of layers including, W film and direct contact layer while coping with any one of such various kinds of structures of the direct contact layer.
Moreover, according to the Inventor's own knowledge, when the direct contact layer 104 is etched, chemical reaction products 107 like titanium fluoride (TiF.sub.x) as shown in FIG. 2 are produced and undesirably remain because of influences of residual fluorine (F) in the etching chamber. These reaction products 107 such as TiF.sub.x invite generation of etching scum 108 on the inter-layer insulating film 102 as shown in FIG. 3, and the etching scum 108 invite a decrease in reliability of the wiring formed on an upper layer.
Furthermore, when the contact plug 106 is formed, different chambers were used for the step of depositing the W film 105, that is, the step of burying W inside the contact hole 103, and for the step of etch-back of the W film 105. Therefore, the process for fabricating the contact plug was inevitably complicated.